Method of producing an electrical heating element and fitting assembly

ABSTRACT

A heating element includes an elongated tubular sheath which confines a resistance wire supported by a thermally conductive electrical insulation material which extends to a position flush with the end surface of the sheath. Each end portion of the heating element is supported by a bulkhead fitting which is formed of sheet metal and includes a tubular wall portion having helical convolutions defining external threads. A radial flange portion projects outwardly from the tubular wall portion and forms an annular tapered hub portion firmly engaging the outer surface of the sheath. The flush end surfaces of the insulation material and the sheath are spaced inwardly from the end surface of the fitting to define a cavity, and a thermosetting sealant material is disposed within this cavity and the space defined between the outer surface of the sheath and the helical convolutions.

United States Patent 1191 Pease *Apr. 2, 1974 [5 METHOD OF PRODUCING AN3,118,124 1/1964 Bleckmann 338 317 ELECTRICAL HEATING ELEMENT AND toilet@I ease FITTING ASSEMBLY 3,676,254 7/1972 Hight et al 156/294 X [76]Inventor: James F. Pease, 1001 Viewpoint Dayton Ohm 45459 PrimaryExaminerCharles W. Lanham 1 i The portion f the term f this AssistantExaminer-Victor A. DiPalma patent Subsequent to APR 1 19 9 Attorney,Agent, or FirmJacox & Meckstroth has been disclaimed.

[22] Filed: Feb. 20, 1973 ABSTRACT [21] Appl. No.: 334,002 A heatingelement includes an elongated tubular sheath which confines a resistancewire supported by a Related Apphcauon Data thermally conductiveelectrical insulation material Division of P- 244,5163 pf 1972, whichextends to a position flush with the end surface 3,732,398 acommuatwnm'pa" of the sheath. Each end portion of the heating element1971 abandoned is supported by a bulkhead fitting which is formed ofsheet metal and includes a tubular wall portion having g 29/611 2helical convolutions defining external threads. A radial flange portionprojects outwardly from the tubular [5 8] held g gg 'g g wall portionand forms an annular tapered hub portion 174 2 b 3 3 9 firmly engagingthe outer surface of the sheath. The l I flush end surfaces of theinsulation material and the sheath are spaced inwardly from the endsurface of [56] References C'ted the fitting to define a cavity, and athermosetting seal- UNITED STATES PATENTS ant material is disposedwithin this cavity and the Rl3,095 3/1910 Ruby 339/130 R space definedbetween the outer surface of the sheath 2,245,602 6/l94l Morris 338/240X and the helical convolutions. 2,630,469 3/1953 Miller 339/l30 R X3,047,910 8/ 1962 Downs 156/294 X 9 Claims, 4 Drawing Figures METHOD OFPRODUCING AN ELECTRICAL HEATING ELEMENT AND FITTING ASSEMBLY RELATEDAPPLICATIONS This application is a division of co-pending applicationSer. No. 244,516, filed Apr. 17,1972 now issued as U.S. Pat. No.3,732,398 and which is a continuationin-part of application Ser. No.194,742, filed Nov. 1, 1971 and now abandoned. This application alsorelates to the invention disclosed in. application Ser. No. 205,200,filed Dec. 6, 1971, now issued as U.S. Pat. No. 3,747,206.

BACKGROUND OF THE INVENTION The present invention is directed to animprovement in the method of producing an electrical heating element andfitting assembly of the type disclosed in U.S. Pat. No. 3,657,519 whichissued on Apr. 18, 1972 on an application which was copending with aboveparent application Ser. No. 194,742.

In the art of electrical heating elements which are used within the sumpof either a commercial or a domestic dishwashing machine, commonly theheating element includes an elongated tubular metal sheath in which anickel-chromium electrical resistance wire is concentrically supportedby a thermally conductive electrical insulation material such asmagnesium oxide. The ends of the wire are attached to correspondingterminal pins which project axially from the end portions of the sheath.A machined metal fitting is commonly brazed or soldered to the endportions of the sheath.

To protect the dry rigid magnesium oxide insulation material andhermetically seal it against moisture, the material is sandblasted ormechanically removed from each end or tip portion of the sheath todefine an annular cavity surrounding the projecting terminal pin. Thiscavity is then filled with a sealant material such as an epoxy resin,for example, as illustrated in U. 8. Pat. No. 3,534,294. Thesesandblasting and filling operations require substantial time and addsignificantly to the cost of producing the heating element.

The above patent application discloses a novel and an improved means forsecuring the end portions of a sheath-type heating element to the wallof a liquid heating tank or vessel. This means includes a tubular bulkhead bushing or fitting which is drawn from sheet metal such as brassand is deformed to define helical convolutions which form externalthreads for receiving a mating drawn sheet metal nut. The bulkheadfitting is secured and sealed to the corresponding end portion of thesheath by soft solder which forms an electrical ground connectionbetween the end portion of the sheath and the fitting so that the sheathcan be grounded through the fitting by a suitable ground wire attachedto the fitting through a ring-type terminal.

SUMMARY OF THE INVENTION The present invention is directed to animproved electrical heating element and bulkhead fitting assembly whichsignificantly reduces the cost of manufacturing the assembly byeliminating operations for preparing the heating element to receive thefittings and by simplifying the assembly of the fittings onto theheating element'and hermetically sealing the heating element all in oneassembly operation. That is, the present invention eliminates the needfor sandblasting the thermally conductive insulation material from eachend portion of the sheath of the heating element and provides forhermetically sealing the insulation material within the heating elementduring the operation of assembling the fitting onto the heating element.The invention also provides a simplified means for forming a positiveelectrical ground between the bulkhead fitting and the endportion of thesheath without soldering the fitting to the sheath. Thus, the inventioneliminates the need for washing the fitting after the solderingoperation to remove the soldering flux, and further provides forminimizing the gauge of the sheet metal which is used for producing thefitting.

The above features and advantages and other advantages of the inventionwill be clearly apparent from the following description, theaccompanying drawing and the appended claims.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a plan view of a heatingelement and fitting assembly constructed in accordance with theinvention and shown mounted on the wall of a liquid heating vessel;

FIG. 2 is an enlarged fragmentary axial section of a heating element andfitting assembly;

FIG. 3 is an enlarged axial section similar to FIG. 2 and illustratingthe method of assembling a fitting onto an end portion of the heatingelement; and

FIG. 4 is an enlarged fragmentary section showing another embodiment ofthe invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The immersion heating element10 shown in FIG. 1 is illustrative of the type commonly mounted withinthe sump of an automatic dishwashing machine for heating water and foralso heating air during the drying period of the washing cycle. Theheating element 10 includes a metallic sheath 12 which is usually formedfrom stainless steel or nickel alloy tubing and has a circularcrosssectional configuration. While the sheath 12 shown in FIG. 1 isgenerally circular, the sheath may be formed in practically anyconfiguration such as, for example, rectangular with rounded corners orserpentine shaped.

The sheath l2 enclosed a high resistance conductor or wire 13 havingends connected to corresponding low resistance terminal pins 14 whichextend concentrically through the end portions 15 of the heating elementto terminal connectors 16. A thermally conductive electrical insulation18 such as magnesium oxide, surrounds the wire 13 and each terminal pin14 and supports the wire and pins concentrically within the sheath 12.

As shown in the above application, each end portion 15 of the heatingelement 10 extends through a corresponding circular hole of opening 19(FIG. 1) formed within a bulkhead or wall 20 such as the wall whichdefines the sump of an automatic dishwashing machine. Each end portion15 of the heating element 10 is secured to the wall 20 by a fittingassembly which includes a tubular bulkhead fitting 25 (FIG. 2) formed bydrawing and deforming a sheet metal disk in successive or progressivesteps. Since the fittings 25 mounted on both end portions 15 of theheating element 10 are identical, only one will be described in detail.

In accordance with the present invention, each fitting 25 includes aflange portion 28 which is partially formed by an outwardly projectingradial flange wall 29. The wall 29 has an outer periphery integrallyconnected to an inwardly projecting radial flange wall 31 which extendsto form a frusto-conical hub portion 32 defining a circular openinghaving a diameter slightly less than the outer diameter of the sheath12.

The fitting 25 further includes a cylindrical wall portion 34 whichextends from the flange wall 29 and which is adapted to receive a rubbergrommet 36 (FIG. 1) mounted within the corresponding opening 19 withinthe wall 20 when the heating element is installed within the wall. Thecylindrical wall portion 34 connects with a tubular wall portion 38having helical convolutions 39 which define corresponding externalhelical treads. As a result of the uniform wall thickness of the fitting25, the convolutions 39 provide the tubular portion 38 with a corrugatedwall configuration in axial cross-section as illustrated in FIG. 2.Preferably the inner diameter of the convolutions 39 is substantiallythe same as the outer diameter of the sheath 12 as shown in FIG. 2. Theconvoluted tubular portion 38 connects with a cylindrical portion 41which preferably also has an inner diameter substantially the same asthe outer diameter of the sheath 12.

As shown in FIG. 2, the end surface 42 of the insulation material 18 isflush with the end surface 43 of the sheath 12, and these flush endsurfaces are located inwardly from the outer end surface 44 of thefitting 25. A water-tight seal is formed between the end portion of thesheath 12 and the bulkhead fitting 25 by a sealant material 45.Preferably, the sealant material 45 consists ofa heat activatedthermosetting epoxy resin. This material fills not only the annularspace or cavity around the terminal pin 14 between the end surface ofthe fitting 25 and the flush end surfaces of the sheath l2 andinsulation material 18, but also fills the space defined between eachconvolution 39 and the outer surface of the sheath 12. The sealantmaterial 45 also fills the space between the parallel walls 29 and 31 ofthe flange portion 28 as well as the space defined between thecylindrical wall portion 34 and the outer surface of the sheath 12.

Referring to FIG. 3, each of the bulkhead bushings or fittings 25 isassembled onto the corresponding end portion 15 of the heating elementin the following manner. The hub portion 32 of the fitting 25 is pressedonto the end portion of the sheath 12 until the sheath projects afraction of an inch into the fitting as indicated in FIG. 3. Apredetermined quantity of heat activated liquid epoxy resin material 45is injected or poured into the fitting 25 so that the material 45 fillsthe space within the flange portion 28 of the fitting and the spaceabove the flush end surfaces of the sheath 12 and insulation material 18to a level as generally indicated in FIG. 3. The fitting 25 is thenpressed further onto the end portion of the heating element 12 until thefitting 25 is positioned as shown in FIG. 2.

During this pressing operation, the epoxy resin material 45 fills thespace between the convolutions 39 and the outer surface of the sheath 12and results in filling the annular space or cavity surrounding theterminal pin 16 between the end surface of the fitting 25 and the flushend surfaces of the sheath 12 and insulation material 18. The heatingelement assembly is then heated within an oven to activate the epoxyresin material 45 and to set the material to a rigid condition forming apositive hermetic seal between the fitting 25 and the corresponding endportion 15 of the heating element 10. When the heating element isinstalled within the tank wall 20, the rubber grommets 36 formwater-tight seals between the flange portions 28 of the fittings 25 andthe tank wall 20 in response to tightening of mating tubular sheet metalnuts 50 threaded onto the tubular portions 38 of the fittings as shownin the above application.

Referring to FIG. 4, a modified fonn of a heating element and fittingassembly includes a tubular fitting 50 having a cylindrical wall portion54 which corresponds with the cylindrical wall portion 34 of the fitting25 shown in FIG. 2 and is adapted to receive the rubber grommet 36. Anoutwardly projecting radial flange portion 56 is connected to thecylindrical wall portion 54 by a curved neck or hub portion 58 whichprojects inwardly from the cylindrical wall portion 54 and firmlyengages the outer surface of the metallic sheath 12. Thus the neck orhub portion 58 serves the same function as the hub portion 32 of theembodiment shown in FIGS. 2 and 3, that is, to confine the sealantmaterial and to provide a tapered or curved lead surface for insertingthe sheath 12 into the fitting 50. In other respects, the fitting isconstructed substantially identical to the fitting 25.

From the drawing and the above description, it is apparent that aheating element and fitting assembly constructed in accordance with thepresent invention, provides desirable features and advantages. Forexample, the bulkhead bushing or fitting 25 or 50 is quickly andeconomically produced from a disc of sheet metal and assembles onto anend portion 15 of a heating element 10 in a manner which eliminates theoperation of sandblasting an annular cavity within the end portion ofthe metal sheath 12 around the terminal pin 14. The epoxy resin materialnot only forms a positive hermetic seal for the end surface of theinsulation material 18, but also forms a water-tight seal between thefitting 25 or 50 and the outer surface of the sheath 12. In addition,the rigid epoxy resin forms a rigid solid mass between the convolutions39 and the end porton 15 of the heating element 10 so that the threadsformed by the convolutions 39 do not collapse or deform when thecorresponding nut 50 is tightened with substantial torque.

The hub portion 32 of the fitting 25 or the hub portion 58 of thefitting 50 not only forms a tapered lead surface receiving the tipportion of the heating element 10 in a press-fit relation, but alsoforms a positive electrical ground connection between the outer surfaceof the sheath l2 and the fitting 25 or 50. Furthermore, the doublewalled flange portion 28 cooperates with the hardened epoxy resinmaterial 45 to provide for minimizing the gauge or thickness of thesheet material used for producing the fitting 25.

While the forms of heating element and fitting assembly herein describedconstitute preferred embodiments of the invention, it is to beunderstood that the invention is not limited to these precise forms ofassembly, and that changes may be made therein without departing fromthe scope and spirit of the invention.

The invention having thus been described, the following is claimed:

I. In a method of producing an electrical heating element assembly formounting within spaced openings of a liquid heating vessel, andincluding the steps of forming an elongated tubular sheath havingopposite end portions, positioning an elongated electrical resistanceelement within the sheath with a thermally conductive insulationmaterial, and extending terminal members from each end portion of theresistance element through the corresponding end portions of the sheath,the improvement comprising the steps of drawing a sheet of metal to-formapair of tubular fittings each having a flange portion and a tubularwall portion, deforming said tubular wall portion of each saidfitting toproduce ahelical convoluted thread portion having a corrugated wallconfiguration in axial cross-section, de-

- forming each said fitting to form an inwardly projecting grippingportion, positioning one of said fittings on eachof said end portions ofsaid tubular sheath with said gripping portion firmly engaging saidsheath, in-

serting a fluid bonding and sealant material into the space definedbetween each said fitting and said sheath,

and allowing said material to harden to form a liquidtight seal betweensaid fitting and said sheath.

2. A method as defined in claim 1 wherein said fluid bonding and sealantmaterial is inserted into the space between said corrugated wallconfiguration and the outer surface of the sheath.

3. A method as defined in claim 1 wherein said fluid bonding and sealantmaterial is confined with said tubular portion of said fitting when saidfitting is positioned onto said sheath.

4. A method as defined in claim 1 including the step of heating saidfitting and said sheath after said bonding and sealant material isinserted into said space to effect rapid hardening of said material.

5. A method as defined in claim 1 wherein the step of deforming eachsaid fitting to form said gripping portion, comprises forming aninwardly projecting annular hub portion having a tapering inner leadsurface, and wherein said hub portion of each said fitting is pressedonto the corresponding end portion of said sheath.

6. A method as defined in claim 5 wherein said hub portion of each saidfitting, is located between said flange portionand said thread portionof said fitting.

7. In a method of producing an electricahheating element assembly formounting within spaced open; ings of a liquid heating vessel, andincluding the steps of forming an elongated tubular sheath havingopposite end portions, positioning. an elongated electrical resistanceelement within the sheath with a thermally conductive insulationmaterial, and extending terminal members from each end portion of theresistance element through the corresponding end portions of the sheath,the improvement comprising the steps of drawing a sheet of metal to forma pair of tubular fittings each having a flange portion and atubularwall portion, deforming said tubular wall portion of each said fittingto produce a helical convoluted thread portion having a corrugated wallconfiguration in axial cross-section, deforming each said fitting toform an inwardly projecting gripping portion, positioning one of saidfittings on each of said end portions of said tubular sheath with saidgripping portion firmly engaging said sheath, inserting a fluid bondingand sealant material into the space defined between each saidfitting andsaid sheath, allowing said material to harden to form a liquid-tightseal between id fi andsaid. shea and, w era asais tflyitl 'bonding andsealant lmaterial is inserted into said space after each said fitting isirifiially started on said sheath and before said fitting is finallypositioned on .L d sheath stmm-..

8. In a method of producing an electrical heating element assembly formounting within spaced openings of a liquid heating vessel, andincluding the steps of forming an elongated tubular sheath havingopposite end portions, positioning an elongated electrical resistanceelement within the sheath with a thermally conductive insulationmaterial, and extending terminal members from each end portion of theresistance element through the corresponding end portions of the sheath,the improvement comprising the steps of drawing a sheet of metal to forma pair of tubular fittings each having a flange portion and a tubularwall portion, deforming said tubular wall portion of each said fittingto produce a helical convoluted thread portion having a corrugated wallconfiguration in axial cross-section, deforming said tubular wallportion of each said fitting to fonn an inwardly projecting annular beadportion, positioning one of said fittings on each of said end portionsform a liquid-tight seal between said fitting and said 9. In a method ofproducing an electrical heating elementassembly for mounting withinspaced openings of a liquid heating vessel, and including the steps offorming an elongated tubular sheath having opposite end portions,positioning an elongated electrical resistance element within the sheathwith a thermally conductive insulation material, andv extending tenninalmembers from each end portion of the resistance element through thecorresponding end portions of the sheath, the improvement comprising tlgsteps ofdrawing a sheet of metal to form a pair of tubular fittings eachhaving a flange portion and a tubular wall portion, deforming saidtubular wall portion of each said fitting to produce a helicalconvoluted thread portion having a corrugated wall configuration inaxial cross-section, deforming said tubular wall portion of each saidfitting to form an inwardly p'rojeiz tiiig'"annular bead portion,positioning one of said fitting on each of said end portions of saidtubular sheath with said head portion engaging said sheath, inserting afluid bonding and sealant material into a space defined between eachsaid fitting and said.

sheath, allowing said material to harden to form a liquid-tight sealbetween said fitting and said sheath, and further including the steps ofterminating said insulation material substantially flush withthe ends ofsaid sheath, locating each of said fittings with said tubular portionprojecting axially from the end of said sheath, and inserting saidsealant material into the space defined between said tubular portion andthe corresponding said terminal member projecting from 1 3E212 of i heh-n--.

1. In a method of producing an electrical heating element assembly formounting within spaced openings of a liquid heating vessel, andincluding the steps of forming an elongated tubular sheath havingopposite end portions, positioning an elongated electrical resistanceelement within the sheath with a thermally conductive insulationmaterial, and extending terminal members from each end portion of theresistance element through the corresponding end portions of the sheath,the improvement comprising the steps of drawing a sheet of metal to forma pair of tubular fittings each having a flange portion and a tubularwall portion, deforming said tubular wall portion of each said fittingto produce a helical convoluted thread portion having a corrugated wallconfiguration in axial cross-section, deforming each said fitting toform an inwardly projecting gripping portion, positioning one of saidfittings on each of said end portions of said tubular sheath with saidgripping portion firmly engaging Said sheath, inserting a fluid bondingand sealant material into the space defined between each said fittingand said sheath, and allowing said material to harden to form aliquid-tight seal between said fitting and said sheath.
 2. A method asdefined in claim 1 wherein said fluid bonding and sealant material isinserted into the space between said corrugated wall configuration andthe outer surface of the sheath.
 3. A method as defined in claim 1wherein said fluid bonding and sealant material is confined with saidtubular portion of said fitting when said fitting is positioned ontosaid sheath.
 4. A method as defined in claim 1 including the step ofheating said fitting and said sheath after said bonding and sealantmaterial is inserted into said space to effect rapid hardening of saidmaterial.
 5. A method as defined in claim 1 wherein the step ofdeforming each said fitting to form said gripping portion, comprisesforming an inwardly projecting annular hub portion having a taperinginner lead surface, and wherein said hub portion of each said fitting ispressed onto the corresponding end portion of said sheath.
 6. A methodas defined in claim 5 wherein said hub portion of each said fitting, islocated between said flange portion and said thread portion of saidfitting.
 7. In a method of producing an electrical heating elementassembly for mounting within spaced openings of a liquid heating vessel,and including the steps of forming an elongated tubular sheath havingopposite end portions, positioning an elongated electrical resistanceelement within the sheath with a thermally conductive insulationmaterial, and extending terminal members from each end portion of theresistance element through the corresponding end portions of the sheath,the improvement comprising the steps of drawing a sheet of metal to forma pair of tubular fittings each having a flange portion and a tubularwall portion, deforming said tubular wall portion of each said fittingto produce a helical convoluted thread portion having a corrugated wallconfiguration in axial cross-section, deforming each said fitting toform an inwardly projecting gripping portion, positioning one of saidfittings on each of said end portions of said tubular sheath with saidgripping portion firmly engaging said sheath, inserting a fluid bondingand sealant material into the space defined between each said fittingand said sheath, allowing said material to harden to form a liquid-tightseal between said fitting and said sheath, and wherein said fluidbonding and sealant material is inserted into said space after each saidfitting is initially started on said sheath and before said fitting isfinally positioned on said sheath.
 8. In a method of producing anelectrical heating element assembly for mounting within spaced openingsof a liquid heating vessel, and including the steps of forming anelongated tubular sheath having opposite end portions, positioning anelongated electrical resistance element within the sheath with athermally conductive insulation material, and extending terminal membersfrom each end portion of the resistance element through thecorresponding end portions of the sheath, the improvement comprising thesteps of drawing a sheet of metal to form a pair of tubular fittingseach having a flange portion and a tubular wall portion, deforming saidtubular wall portion of each said fitting to produce a helicalconvoluted thread portion having a corrugated wall configuration inaxial cross-section, deforming said tubular wall portion of each saidfitting to form an inwardly projecting annular bead portion, positioningone of said fittings on each of said end portions of said tubular sheathwith said bead portion engaging said sheath, inserting a fluid bondingand sealant material into a space defined between each said fitting andsaid sheath, and allowing said material to harden to form a liquid-tightseal between said fitting and said sheath.
 9. In a method of producingan electrical heatIng element assembly for mounting within spacedopenings of a liquid heating vessel, and including the steps of formingan elongated tubular sheath having opposite end portions, positioning anelongated electrical resistance element within the sheath with athermally conductive insulation material, and extending terminal membersfrom each end portion of the resistance element through thecorresponding end portions of the sheath, the improvement comprising thesteps of drawing a sheet of metal to form a pair of tubular fittingseach having a flange portion and a tubular wall portion, deforming saidtubular wall portion of each said fitting to produce a helicalconvoluted thread portion having a corrugated wall configuration inaxial cross-section, deforming said tubular wall portion of each saidfitting to form an inwardly projecting annular bead portion, positioningone of said fittings on each of said end portions of said tubular sheathwith said bead portion engaging said sheath, inserting a fluid bondingand sealant material into a space defined between each said fitting andsaid sheath, allowing said material to harden to form a liquid-tightseal between said fitting and said sheath, and further including thesteps of terminating said insulation material substantially flush withthe ends of said sheath, locating each of said fittings with saidtubular portion projecting axially from the end of said sheath, andinserting said sealant material into the space defined between saidtubular portion and the corresponding said terminal member projectingfrom the end of said sheath.